The invention concerns a circular knitting machine with a support disk and needle cylinder attached to it with screws,
Known circular knitting machines of this type, if designed as high-performance machines (for example, cylinder diameter 762 mm, 45 rpm, 96 systems), can heat up strongly, especially in the region of the cam and cylinder. The temperature differences caused by this lead to different heat expansion between the individual components. Numerous expedients are therefore already known, with which it is possible to compensate for different heat expansions. Such expedients are used, for example, to compensate for radial expansion in the region of the bearings of the generally annular support disks that carry the needle cylinders (DE 28 29 678 C2), to compensate for different radial heat expansion between the needle cylinders and sinker rings (DE 33 16 382 C2), to avoid deformation of the cam rings (DE 34 28 855 C2), or to compensate for axial displacements that can result in undesired changes in comb spacing, i.e., the spacing between the needle cylinder and dial in the knitting region (DE 41 28 372 A1).
It has now been found that different heat expansions in the lower region of the needle cylinder can also occur, especially where it is connected to the support disk. Temperature differences of 25xc2x0 C., for example, are reached between these two parts, especially during running up of the circular knitting machine. One reason for this is probably poor heat transfer between the needle cylinder and the support disk, since the needle cylinder is attached to the support disk with only a few, for example six, screws distributed in the peripheral direction and does not or only inadequately liexe2x80x94in the regions lying between the fastening sitesxe2x80x94on the support disk especially if additional washers are used. As a result, the needle cylinder is heated more strongly than the support disk, and is therefore deformed radially more strongly than the disk. Significant stresses are created between the two components, which lead to strong distortion, especially in the needle cylinder, since it can buckle and bulge convexly in uncontrolled fashion between the fastening sites. If the friction force in the region of the fastening sites is no longer sufficient, the needle cylinder breaks off at one or more fastening sites, so that persistent radial displacements are produced between the needle cylinder and support disk that lead to unroundness of the needle cylinder. Such eccentricities lead to different spacings between the needle cylinder and the cam surface surrounding it during operation of the circular knitting machine, to different spacings between the knitting needles situated in the needle cylinder and the thread guides mounted in the machine frame, and therefore to an adverse effect on the quality of the knitwear being produced. Different comb spacings can also be produced by this.
Experiments have surprisingly led to the result that is problem cannot be avoided simply by using more and/or stronger screws for fastening of the needle cylinder to the support disk. Compensation means of the type described above might be of additional help, but would lead to costly design solutions and to solutions not always desired for other reasons. This is particularly true when an attempt is made to improve heat transfer between the needle cylinder and support disk, because this would lead to warping in the region of the bearings of the support disk and the means of compensation would have to be provided in the bearing region (DE 28 29 678 C2).
It is, therefore, an object of this invention to design a circular knitting machine of the generic type mentioned above so that critical roundness errors are avoided.
A further object of this invention is to design the knitting machine specified above such that the needle cylinder can expand substantially uniformly in a radial direction if temperature differences between the needle cylinder and the support disk occur.
Yet another object of this invention is to provide a circular knitting machine having a needle cylinder and a support disk therefor with simple means for compensating different radial expansions between the cylinder and the disk.
These and other objects are solved in accordance with this invention by means of an intermediate ring between the support disk and the needle cylinder which ring is elastically deformable in the radial direction.
Advantages of this invention are that the region between the needle cylinder and the support disk is configured elastically, so that this region can match with the expanding needle cylinder, and that the stresses (forces) in the screw connections become smaller. On this account, the needle cylinder can expand radially more uniformly, avoiding buckling and breaking.
Additional advantageous features of the invention are apparent from the subclaims.